The present invention relates to a medical implant, more particularly to a medical implantable device comprising a magnetic nuclear resonance spectrometer arrangement capable of characterising and monitoring the local flow rate of a physiological fluid as well as its chemical composition.
Nuclear magnetic resonance is based on the following known principle. All atomic nuclei with an odd atomic mass or an odd atomic number (like hydrogen for example) possess an intrinsic nuclear magnetic momentum. Without entering the details, one can consider that this momentum is generated by the rotation of the proton around the nucleus. When a NMR active nucleus is placed in a static magnetic field, this momentum can take two different orientations. The momentum may take either an orientation parallel to the magnetic field or an antiparallel orientation relative to the magnetic filed. Considering a population of hydrogen atoms immersed in the same static magnetic field, the number of atoms having a parallel orientation is slightly greater than the number of atoms having an antiparallel orientation. This is due the fact that the parallel orientation is energetically more favourable. The passage from the parallel state to the anti parallel state occurs when the atoms absorb electromagnetic energy at a given frequency called the resonance frequency. This resonance frequency depends on the nucleus of the atom and on the intensity of the static magnetic field. A magnetic nuclear resonance apparatus works by analysing the signal emitted during the transition from the excited state (anti-parallel) to the state of equilibrium (parallel). The nuclei are placed in a high intensity static magnetic field and then exited with an electromagnetic wave having a frequency corresponding to the resonance frequency. When the return to the equilibrium state occurs, a signal having the same frequency as the excitation signal (resonance) is generated and can be measured thanks to an antenna.
The resonance detection may occur either at the stage of excitation, by measuring the energy absorption by scanning a range of frequency or when the atoms return to the state of equilibrium. In the later, one measures the electromagnetic signal emitted by the magnetic momentum returning to their equilibrium position. If other atoms than hydrogen atoms are present in the solution to be characterised, the spin of their electrons will generate a magnetic field at the microscopic level. Thus the hydrogen atoms are submitted to the static magnetic field generated by the NMR device to which is superposed locally the magnetic field generated by the electrons. This will alter the resonance frequency with a signature specific to the environment of the hydrogen atoms within the solution to characterise. Nuclear magnetic resonance spectroscopy is based on this principle and is mainly used for two different kind of applications, namely for biochemical analysis in laboratories and in magnetic resonance imaging spectroscopy. In laboratories, nuclear magnetic resonance spectroscopy is usually performed at very high magnetic field intensity ( greater than 10 Tesla) to reveal the atomic structure of molecules. In contrast magnetic resonance imaging spectroscopy (MRIS) is performed with standard MRI equipment at lower filed intensity (around 1.5 Tesla) to reveal the composition of the tissues environment at molecular level.
It is also possible to gather information related to the flow of a liquid by analysing the signal returning to the equilibrium state after a resonant excitation. This signal has a decrease, which is characteristic when the liquid is static, and a faster decrease when the liquid is in movement. This is due to the fact that part of the excited atoms will leave the detection volume of the antenna. This technique also used in magnetic resonance imaging spectroscopy devices.
Chronic monitoring of specific chemical compounds in a body fluid as well as gathering information relative to the flow rate of a fluid within the human body is a key in many areas of medicine, this is particularly true for brain metabolites monitoring in trauma patient or for monitoring the flow rate of the cerebrospinal fluid in a shunted hydrocephalic patient. The known techniques for monitoring the concentration of specific chemical compounds in a physiological fluid are usually achieved invasively either by techniques that require taking samples of the fluid (dialysis, . . . ) or by inserting probes in the targeted fluid/tissue (micro dialysis, blood gas analysis.) These techniques involve either a puncture for each sample to analyse or a catheter line to be left in place for the duration of the monitoring. Furthermore, invasive catheter probes are mainly targeted to specific analytes such as O2, CO2, glucose or lactose.
Other non-invasive techniques such as magnetic resonance imaging spectroscopy are rather expensive and do not permit a continuous monitoring. Moreover, concerning the flow rate assessment, there are currently no known devices to perform these measures in situ.
The aim of the present invention is to remedy the aforesaid drawbacks. This goal is achieved by an implantable nuclear magnetic resonance spectrometer for measuring the chemical composition of a fluid or for measuring the flow rate of the fluid. The spectrometer includes a housing and a catheter traversing across the housing so that a fluid external to the housing may flow through the catheter within the housing. A permanent magnet is disposed within the housing and generates an intense homogenous magnetic field in the vicinity of the catheter. An electronic circuit is disposed within the housing for detecting and formatting a nuclear magnetic resonance excitation signal. An excitation coil is connected to the electronic circuit and is disposed about the catheter to expose the fluid within the catheter to the excitation signal and to collect the nuclear magnetic resonance excitation signal.
Yet another objet of the invention is the use of said implantable nuclear resonance spectrometer in several medical applications.
Further features and other objects and advantages of this invention will become clear from the following detailed description made with reference to the accompanying drawings illustrating in a schematic and non-limiting way one embodiment of the implantable nuclear magnetic resonance spectrometer.